The National Institute of Mental Health Panic Disorder Questionnaire (NIMH-PQ) is a research tool developed by the Section on Anxiety and Affective Disorders (SAAD). The NIMH-PQ was designed to assess the longitudinal course and component features of panic disorder, and demographic and epidemiologic variables in panic disorder. To date, data have been collected from greater than 1200 individuals in the United States, as well as hundreds of individuals in foreign countries. Using the NIMH-PQ, it has been determined that the DSM-IV time criteria for panic attacks (i.e., that panic attacks must reach peak intensity within 10 minutes) is not a useful criteria for defining panic disorder. In particular, individuals whose typical panic attacks reach peak intensity in greater than 10 minutes are as disabled (or in some cases, more severely impaired) as those whose panic attacks reach peak intensity in less than 10 minutes. The NIMH-PQ has also been used to determine that "pure" agoraphobia (i.e., agoraphobia without panic disorder) is exceedingly rare, and possibly non-existent. According to data collected using the NIMH-PQ, approximately 60% of individuals with panic disorder suffer from sleep panic.